1,2,4-Trichlorobenzene is frequently produced by chlorinating benzene, chlorobenzene and/or ortho-dichlorobenzene and, less frequently, by chlorinating meta-dichlorobenzene. The formation of 1,2,4-trichlorobenzene is accompanied by the formation of various by-products such as 1,2,3-trichlorobenzene, more highly chlorinated materials including 1,2,4,5-tetrachlorobenzene and 1,2,3,4-tetrachlorobenzene, and sometimes degradation products. The coproduced by-products are undesirable in that they represent losses of one or more reactants to less beneficial materials than the desired 1,2,4-trichlorobenzene. In order to improve the production of 1,2,4-trichlorobenzene, the chlorination is usually conducted in the presence of a catalyst such as ferric chloride, with or without a promoter such as, for example, carbon disulfide, sulfur chloride, or elemental sulfur. R-values, hereinafter more fully defined, on the order of about 1.5 when the x-value, also hereinafter more fully defined, is about 3, are typical of such catalyzed reactions. The quantities of by-products, however, are still undesirably high.